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Poke around on there website. They have lots of different versions of this thing. How it works is by reading the hi and low canbus signals from the car and then it triggers an output of 12vdc, which could be used to run a relay. Not sure how familiar you are with canbus but it is one of the communication signal the vehicle uses to talk to all the onboard computers and sensors. A common example of what this could be used for is if you wanted additional highbeams mounted in your grill. This device would sense the signal of you turning the highbeams on, or them automatically turning on if you have that feature, and then send a 12v signal out the output wire which could be used to close a relay to turn on your additional lights. Basically it makes accessories work as if they are part of the factory wiring.
So in your case you would want to make sure you got one of the products that has the ignition signal sensing. You would then take the output wire for that and attach it to whatever needs that signal. I am guessing that would be your dc2dc charger.
Originally Posted by Adamalli
You could do the above with fuse tap. There is a fuse in the boot fuse box, I think it is the top left fuse, that is only on when the ignition is on. But you have to drill/file a hole to get the wire out. The canbus solutions much cleaner.
Thank you very much. After I posted I looked into it, your explanation summarizes what I read very well, thank you. I've sent an email to the guys at Canm8 to ask about doing a potential custom one (which apparently they do), for my Defender. Interestingly, they also have a contactless reader, which allows you put their canbus reader in a way that does not require you to cut any of the canbus wiring or to use the wiring loom expansion splitter from powerfuluk (not that there is anything wrong with that way of doing it, I just think it would be a slightly cleaner way of doing it).
Thank you for posting this, learned a lot today about this and hopefully I can put it to use as I design my dual batter set up.
This is a great thread with tons of information. I am headed down the path of a second battery system mainly to power a refrigerator. However I think I want to add a couple lights in the interior and maybe the ability to charge a phone or two. Lots of great ideas her. I do have one question I am hoping someone will have insight on.
Has anyone tried two small 12v batteries with maybe a 50ah rating connected in parallel to make the system still 12v and to double the capacity? My thought is maybe two small batteries would open up more mounting options with the MHEV components? Maybe this is not possible? I know you can hook deep cycle batteries in series to increase voltage like my golf cart but is there issues doing parallel?
Ok several questions. Also does it have to be deep cycle batteries? I understand the use of them for RV applications but in a system that gets charged every time your vehicle is running would a standard 12v auto or even motorcycle battery work?
Which Ground did you use for an external dc to dc charger?
Originally Posted by drcoop
So as I continue on my quest to a dual battery setup, I've been tinkering to learn more about the 48v MHEV battery setup... In hopes that the 12v connection in the under-cargo space will offer an acceptable "hot wire" instead of having to tunnel under the floor to get to the main battery (as a few brave and motivated souls have done here, kudos!).
Looking through my workshop manual, I found out that there's a DC to DC converter/charger in all that underfloor mess and this is what it says:
"The DC/DC is supplied with power from the MHEV battery. The DC/DC converts the MHEV battery voltage from approximately 48V DC to the 12V DC for the following: All the vehicles 12V systems. The startup battery. The output from the DC/DC charges the startup battery and provides all the electrical power for all the 12V components. The output from the DC/DC is approximately 14V.
The DC/DC supplies all the power for the startup battery. The DC/DC power for all the vehicle 12V systems in all Power Modes except in Power Mode 0 (vehicle locked and armed)."
Many of you may have known this already, but I had assumed that the power flowed the other way. So with this information, it seems that the alternator must charge the 48V battery and then it's voltage is converted to 12v by the DC DC charger and sent on to the main starter battery and all the 12v systems. Leading me to believe that the current coming out of the DC DC charger must be the same as the starter battery. Therefore plugging in to the large (4ga) cable coming out of the DC DC charger should be safe since its nearly the same as plugging into the starter battery itself. I would obviously put a 80-100amp ANL fuse between this connection point and my own DC DC Charger (which I don't think I'll go any larger than a 40amp Renogy or similar and I'll be sure to protect it with the built in limiter). And since there seems to be current coming from this point up until you lock the doors, I'll be sure to include an ignition source to shut down my DC DC when appropriate.
I did some voltage tests with the car in various conditions that I'll show below along with my understanding of the voodoo electronics:
I have a Bluetti Charger 1 that I want to hook up to the 12v under the floor on my p400. Did you use the GRD next to the Red cable on the left or the Earth Ground on the left next to the Lithium Battery?
